344 CHESTER H. HEUSER 



DESCRIPTION OF THE GASTRO-INTESTINAL TRACT 



Stomach 



In the embryo: The stomach in the late embryo is, in general, 

 pyriform in shape, being shghtly compressed from above down- 

 ward; it lies almost in a transverse zone in the left side of the 

 body. As seen in dissections of the viscera in situ, the stomach 

 is found to be entirely masked by the liver, except on the left 

 where a small portion of the greater curvature projects below 

 the hepatic border (fig. 5) . Upon removing the liver, the stomach 

 may be seen in its characteristic pyriform shape as shown in 

 figures 7 and 9. The greater curvature is about eight times that 

 of the lesser, as determined by measurements of the curves from 

 the esophageal opening to the pylorus. The esophagus enters 

 the stomach at about the middle of the lesser curvature in rather 

 close proximity to the duodenal opening. The pyloric portion 

 is not drawn out into a tubular form as in human embryos 

 (Lewis, '12), and externally at least there is no indication of a 

 pyloric antrum. The blind pouch above the entrance of the 

 esophagus — the fundus (fig. 9) — is relatively long and tapers 

 rapidly upward to its tip. Except that the pyloric portion is 

 not tubular in form, the stomach as a whole has the appearance 

 of the organ in the late rat and early pig embryos. In naming 

 the various subdivisions of the stomach the terms adopted by 

 Lewis ('12) have been used. 



The external surface of the stomach is smooth, but faintly 

 delineated folds in the mucosa can be seen through the outer 

 layers. These folds of the mucosa, or rugae, are in general 

 arranged longitudinally and extend from the fundus down into 

 the corpus, being more prominent along the greater curvature. 

 They are filled with loose embryonic mesenchyme and extend 

 far out into the lumen so that irregularly shaped projections and 

 compartments are evident in sections (fig. 11). 



In the pouch-young: The stomach in the pouch-young is no 

 longer compressed as in the embryo, but has become tremen- 

 dously distended by constant filling with milk. The greatly 

 enlarged organ may be made out in the living animal because of 



